1. Field of the Invention
This invention relates in general to a method and apparatus for transferring images to cylindrical surfaces or cylindrical objects and more particularly to the sublimation transfer of images to a mug by means of the application of heat and a controlled amount of pressure.
2. Description of Related Art
One method of decorating cylindrical articles comprises the use of sublimation transfer techniques involving the printing of a design on a paper backing sheet by conventional printing techniques with sublimation inks, and transferring such designs under heat and pressure to a substrate. During the process, the dyes vaporize from the backing sheet and condense on the cooler substrate to form a brilliant image.
To properly affix the image, uniform pressure and temperature must be applied over the entire expanse of a decal containing the image and, in turn, over that cylindrical portion of the mug that is overlaid with the decal. Prior art processes press a rigid, bulky, heated, curved, metal casting to one side of the cup-shaped portion of the mug, or hinge together two such metal castings and press the latter toward opposite sides of the cup-shaped portion of the mug.
Although the use of curved castings is generally satisfactory for its intended purpose of applying an image on a curved surface, such curved castings have not proven altogether satisfactory. First, it is often desirable to apply large decals to the mug, i.e. those which extend around the cup-shaped portion over an arc length greater than 180.degree.. The known castings can only effectively apply small decals to one or a plurality of areas on the cup-shaped portion of the mug. Typical prior art process do not permit mugs of different sizes to be accommodated in a single apparatus. An 8-oz. mug requires a different clamping device than a 12-oz. mug due to their different radii of curvature. As a result, the different clamping devices can only readily handle a single mug size. Different clamps of different sizes with adjustably would be required to handle different sized mugs.
In an effort to overcome the deficiencies of the process described, some prior art devices presently have used flexible straps to compensate for the different curvature and diameters of the cylindrical substrates that can be accepted. These attempts to solve these problems have not been entirely successful. U.S. Pat. No. 4,874,454 and U.S. Pat. No. 5,019,193 disclose devices for transferring sublimation decals to mugs using a flexible electrical heating pad. These devices are limited, however, in the amount of pressure that can be applied to the mug as a function of the diameter of the mug, with out making separate adjustments for various mug diameters.